This invention relates generally to buried long period gratings, and, more particularly, to an improved method of manufacturing such buried long period gratings.
As lasers have been improved through the years, their use has been extended into a great number of new areas. By expanding the use of lasers into various complex optical systems such as tracking, communications, etc, the optical components used with these lasers require improvement. For example, one such optical component which has great applicability in newly developed laser systems is a component capable of transmitting as well as reflecting light. Such a component is more commonly referred to as a beam splitter.
Unfortunately, the conventional beam splitter is generally unacceptable in high energy laser systems since it suffers from mechanical failure due to absorption or laser radiation which converts to heat. Recently, the blazed or buried long period grating (BLPG) has been developed as an optical component which overcomes problems generally associated with beam splitters. The BLPG is an optical component which provides reflection of high energy laser radiation, refraction of various other optical wavelengths, and removal of absorbed energy by coolant flow. Examples of typical buried long period gratings can be found in the following articles; Chi, Changhwi, "Spectral Shaped Aperture Component," SPIE, Vol. 240, 1980, pgs 185-200 and Chi, C. H. et al, "Buried long period grating for laser applications," SPIE, vol 240, 1980, pgs. 211-222.
The buried long period grating provides a period so large that the grating facet becomes a mirror for the wavelength of interest, thereby minimizing diffraction effects. In general, the long period grating is placed on a cooled metal substrate (for example, molybdenum), buried within a transparent, thermally conductive material, and overcoated with a multilayer dichroic coating that reflects the high energy laser beam and transmits beams of other wavelengths. Since the grating facet of the BLPG is a mirror, the buried long period grating exhibits a large number of desirable characteristics such as: high efficiency, insensitivity to polarization and wavelength, operability over a wide spectral range, minimization of spectral dispersion, and ease of alignment.
Although there are a number of ways to fabricate the blazed or buried long period grating, each method heretofore in use introduces problems associated with material stability, machining tolerances and heat transfer. These problems have substantially affected the acceptability of the blazed or buried long period grating. As a result, it is readily apparent that there exists a great need to improve the fabrication techniques heretofore utilized in the manufacture of the buried long period grating.